This invention relates generally to power tools and more specifically to a power pack charging system for a power tool.
It is generally known to employ rechargeable and removable power packs for use with hand-held, cordless power tools. For example, reference should be made to the following U.S. Pat. No. 5,718,985 entitled "Battery Pack Retaining Latch for Cordless Device" which issued to Bunyea et al. on Feb. 17, 1998; U.S. Pat. No. 5,620,808 entitled "Battery Pack for Cordless Device" which issued to Wheeler et al. on Apr. 15, 1997; and U.S. Pat. No. 5,391,972 entitled "Cordless Tool Battery Housing and Charging System" which issued to Gardner et al. on Feb. 21, 1995; all of which are incorporated by reference herein.
While traditional power pack electrical connectors and chargers having proven sufficient for use with nickel cadmium ("NiCd") battery power packs, the more recently developed nickel metal hydride ("NiMH") battery power packs require a different charging circuit. Accordingly, it is not recommended that nickel metal hydride power packs be charged in a nickel cadmium charger. Charging incompatibility could lead to damaged power packs. Furthermore, nickel metal hydride power packs require an additional temperature terminal to enable the temperature of the batteries to be monitored during charging.
Other traditional battery-to-charger constructions are known which either electrically detect different battery types or only receive a specifically constructed battery case configuration. Such devices are described in U.S. Pat. No. 5,602,454 entitled "Battery Pack having Identification Recesses and Terminals" which issued to Arakawa et al. on Feb. 11, 1997; U.S. Pat. No. 5,200,690 entitled "Quick Charge Control Apparatus and Control Method Thereof" which issued to Uchida on Apr. 6, 1993; and European Patent Application No. EP 0 707 350 A1 entitled "Battery Device and Loading Device for Battery Device" which was published on Apr. 17, 1996. However, these devices are used with video tape recorder cameras or portable computers. Moreover, these conventional chargers and power packs use complicated and expensive electronic circuitry to detect the battery type and do not appear to provide one way charger compatibility for multiple battery types in a simple, economical and mechanical manner.